Abstract: A power drive unit for operation of structure in opposite directions, such as aircraft structure and, particularly, thrust reverser structure of an aircraft engine operable between stow and deploy positions, including, a bi-directional hydraulic motor having a variably positionable wobbler for controlling displacement of the motor. Control structure includes a valve for causing fluid flow through the motor in either of two directions, a control cylinder and piston connected to the wobbler for setting the motor at either minimum or maximum displacement conditions or at any condition therebetween, a servo valve operable for setting the position of the piston in the control cylinder, and a differential area piston operatively connected to the servo valve for positioning thereof and responsive to the pressure drop across the motor in either direction of operation thereof to set the motor displacement at the least value possible for the load condition on the motor.